Many roads, highway, driveways, parking lots and similar structures are paved with an asphaltic composition. Asphaltic pavement is generally made from aggregate, such as rock, shells, recycled pavement materials and other similar materials, and a binder material containing asphalt, tar and other binder materials, as well as various additives, fillers and the like.
In constructing pavement structures with one or more asphaltic layers, it is often necessary to lay each asphaltic layer down on a preceding pavement layer in a predetermined sequence, with a bonding material between the layers. The bonding material, which also may be referred to as a tack coat, acts to provide a degree of adhesion or bonding between the layers, and in some instances, may fuse the layers together. The tack coat also acts to reduce slippage and sliding of the layers relative to other layers in the pavement structure during use or due to wear and weathering of the pavement structure.
Pavement and road surfaces also require regular maintenance to repair normal wear and tear of the roadway due to vehicular or pedestrian traffic, the effect of weather and environmental conditions, and other factors. In some applications, all or a portion of the traffic bearing surface may be removed through grinding, stripping or other means, and a new pavement layer is applied to the prepared structure. In other applications, a new pavement layer is placed down on top of the existing pavement structure to provide a new or renewed traffic-bearing surface. To prepare such preexisting pavement structures for application of an additional, new pavement layer, a tack coat often is applied to the preexisting pavement surface to facilitate the adhesion and/or fusion of the new pavement material with the preexisting surface and/or structure.
A bonding or tack coat also may be applied to a base or substrate layer in advance of the application of the next pavement layer. During such process, construction or other vehicles are expected to travel over the tack coat without significantly damaging or reducing the effectiveness of the coating. Such damage often occurs, however, when the bonding or tack coating is picked up on the tires or tracks of vehicles traveling over the coated surface. Where this occurs, the asphalt compositions often are tracked onto other pavement surfaces causing disruption to the surrounding area. This tracking also reduces the effectiveness of the tack coat by displacing a portion of the intended coating volume from the area awaiting a new pavement layer.
U.S. Pat. Nos. 7,503,724 and 7,918,624 to Blacklidge et al. (the disclosures of which are both incorporated herein by reference) disclose the generally accepted industry practice for applying a tack coat of an asphalt emulsion between adjacent asphalt pavement layers. Blacklidge et al. discloses a tack coat emulsion comprising a first phase, which includes an asphalt composition and a second phase comprising water and emulsifying and stabilizing additives. The first phase of the emulsion comprises hard pen asphalt of about 30% to about 70% by weight of the total emulsion. The asphalt has a pen value of about 5 dmm to about 15 dmm. The second phase of the emulsion comprises 30% to 70% of the total weight of the total emulsion. The second phase also includes emulsifiers, stabilizers and other additives comprising about 0.1% to about 3% by weight of the total emulsion. Other additives are disclosed by Blacklidge et al. as “common polymers such as EVA, SBS, SB, SBR, SBR latex, waxes, polychloroprene, isoprene, polybutadiene, acrylic and acrylic copolymers, carbon reinforced elastomers, ground tire rubber, and/or other elastomers and plastomers to assist in obtaining desired breaking rates for the emulsion and adhesion of the asphalt emulsion residue.” Blacklidge et al. discloses that its product is applied to paving substrate layers or asphalt base layers to improve adhesion and to reduce slippage of adjacent layers. Blacklidge et al. also discloses that the cured tack coat has the property of reduced tracking. The tack coat emulsion is applied at ambient temperatures or at a temperature of about 140 to about 180° F. Blacklidge et al. discloses that the tack coat emulsion dries in about 5 to about 30 minutes and cures in about 30 minutes to about one hour. Heated asphalt paving material is then applied on top of the cured tack coat to form an asphalt pavement layer.
U.S. Pat. No. 8,764,340 to Campbell (the disclosure of which is incorporated herein by reference) discloses a trackless tack coat emulsion. Campbell's emulsion comprises asphalt, water and an anionic emulsifying agent to provide an anionic asphalt emulsion. The asphalt emulsion is applied at a temperature of approximately 110 to 160° F.
U.S. Pat. No. 8,968,457 to Payne (the disclosure of which is incorporated herein by reference) discloses a cationic asphalt tack coat material. Payne's tack coat emulsion comprises asphalt, water, a latex polymer, sodium chloride, muriatic acid and a surfactant wherein the composition is a cationic emulsion. The asphalt emulsion is applied at a temperature of 160° F. as a tack coat. Payne does not disclose what polymer is used for the latex in his asphalt emulsion.
Blacklidge et al., Campbell and Payne all purport to provide compositions having reduced tracking compared to the prior art process of applying a liquefied asphalt composition, which included solvents and/or volatile oils, such as naphthas or kerosenes. However, those prior art tack coating materials are not truly trackless. It would therefore be desirable to provide an improve tack coat emulsion having reduced tracking properties and rapid drying and curing.